1. Technical Field
The present invention relates generally to automatic transmission control for an automotive vehicle and, more particularly, to an acceleration based shift control strategy for controlling the gear shifting of an automatic transmission.
2. Discussion
Automotive vehicles generally incorporate a motive force system having three basic components: an engine, a powertrain and wheels. The engine produces force by converting chemical energy from a liquid fuel into the mechanical energy of motion. The powertrain transmits the resultant force of this kinetic energy to the wheels which frictionally contact a surface for moving the vehicle. The main component of the powertrain is the transmission, which transmits engine torque over a relatively limited angular speed range to the wheels over a broader speed range, in accordance with the tractive-power demand of the vehicle. The transmission also controls the direction of rotation applied to the wheels so that the vehicle may be driven both forward and backward.
One advanced type of transmission is a four speed electronically controlled automatic transmission with overdrive. Examples of this type of electronically controlled automatic transmission are described in U.S. Pat. No. 4,875,391, entitled "An Electronically-Controlled, Adaptive Automatic Transmission System", issued on Oct. 24, 1989 to Leising et al; U.S. Pat. No. 4,905,545, entitled "Method of Controlling the Speed Change of a Kickdown Shift for an Electronic Transmission System", issued on Mar. 6, 1990 to Leising et al and U.S. Pat. No. 4,951,200, entitled "Method of Controlling the Apply Element During a Kickdown Shift for an Electronic Automatic Transmission System", issued on Aug. 21, 1990 to Leising et al. These patents are owned by the Assignee of the present application and are incorporated herein by reference. However, it should be appreciated that the principles of the present invention are not limited to any particular automatic transmission, whether electronic or hydraulic controlled and that the present invention may be applied to a wide variety of other powertrain configurations.
Automotive vehicles are commonly equipped with electronic control systems such as a powertrain control system for controlling the operation of the engine and drivetrain of the vehicle. The electronic powertrain control system includes a microcomputer-based transmission controller capable of receiving and monitoring input signals indicative of various vehicle operating conditions such as engine speed, torque converter turbine speed, output vehicle speed, throttle angle position, brake application, hydraulic pressures, a driver selected gear or operating condition (PRNDL), engine coolant temperature and/or the ambient air temperature. Based on the information contained in the monitored signals, the controller generates command or control signals for causing actuation of solenoid-actuated valves to regulate the application and release of fluid pressure to and from apply cavities of clutches or frictional elements of the transmission. Accordingly, the transmission controller is typically programmed to execute predetermined shift schedules stored in memory of the controller through appropriate command signals to the solenoid-actuated valves.
In some conventional automatic transmission control routines, the use of a predetermined shift schedule provides allowable gear shifts based on a speed value and percentage of throttle opening. An automatic transmission gear upshift generally follows a predetermined upshift curve, while a transmission downshift follows a predetermined downshift curve. The upshift and downshift shift points are determined as a function of output shaft speed and percentage of throttle opening and are commonly obtained from the upshift and downshift curves. With the conventional approach, the shift points remain constant as long as the vehicle can maintain the desired shift speed.
Conventional automatic transmission gear shifting approaches provide shift points that compromise for various possible loads on a vehicle. For example, a vehicle that is lightly loaded may realize a shift point that occurs later than desired because of compromises taken into consideration for heavier vehicle loading conditions. Moreover, this problem is amplified for downhill vehicle travel conditions. Similarly, for a vehicle that is heavily loaded, the shift points are generally compromised for lighter vehicle loading conditions, and this may result in lugging of the engine. This is especially true for heavily loaded vehicles traveling uphill and can lead to a gear "shift hunting" condition in which an upshift gear does not provide sufficient torque to maintain vehicle speed and results in cyclical upshift and downshift gear changes.
It is therefore one object of the present invention to provide for a system and method of controlling gear shifting of an automatic transmission for a motor vehicle in a manner that is adaptive to vehicle loading conditions.
It is another object of the present invention to provide for such a system and method of controlling automatic transmission upshifts that adapts to heavy vehicle load increases.
It is also an object of the present invention to provide for such a system and method of controlling downshifting of the automatic transmission taking into consideration lessened vehicle load conditions.
Further, it is another object of the present invention to monitor torque and vehicle load and predict available acceleration to control transmission gear shifting of an automatic transmission to accommodate for different load conditions on the vehicle.